Discovery of a pipe with a high level of plutonium-239 at a clean-up site at Los Alamos National Laboratory has forced officials to shut down operations.

The pipe, which was dug up by an excavator three weeks ago, had plutonium-239 that exceeded the amount lab officials had expected and that was allowed above the ground, lab spokesman Fred deSousa said Friday.

The lab had estimated about 200 grams of plutonium-239 over the 6-acre clean-up site. The pipe alone alone had 42 grams, or about 1.6 ounces.

"We knew going into the project that this is a former hazardous waste and radioactive matieral landfill, so to pull up an object like this is not necessarily a surprise to us," deSousa said. "What is unique is the concentration."

Safety measures already in place worked, he added. For instance, the site includes fixed metal buildings, no digging in open air and protective suits with air supplies for workers.

Work on the site could be reactivated as early as Friday afternoon or by the weekend, deSousa added.

"We're in the latest stage of the readiness review," he said.

That means the lab has looked at its safety procedures, studied the incident and why it ended up over the limit; and what steps it can take to make sure this doesn't happen again.

As a result of the examination, an additional safety step has been tacked on. A radiation detector that had been on the ground next to the hole will be placed directly on the arm of the excavator.

"We put the radiation detection device on the arm of the excavator that looks down into the hole in which they are digging," deSousa said. "We will be able to detect something even before we bring it out of the hole."